Transponder arrangement

ABSTRACT

The invention concerns a transponder arrangement in which the transponder is disposed on a conductive surface. According to the invention, the coils forming the transponder antenna are aligned at a slight distance from the metal surface with their main magnetic field direction parallel to this surface.

FIELD OF THE INVENTION

The present invention pertains to a transponder array with a transponderarranged on a conductive surface.

BACKGROUND OF THE INVENTION

Transponders, which are able to exchange data with a polling device viaalternating electromagnetic fields, are suitable for the contactlesspolling of information stored on a movable data storage medium. Thecoupling with the electromagnetic fields is performed, at least on thetransponder side, preferably via magnetic dipole antennas, especiallyair core coils or ferrite antennas.

For example, a device for the recognition of objects, especially motorvehicles, in which flat antennas of a polling station are recessed intothe ground with their antenna surfaces in parallel to the road surface,has been known from DE 40 39 690 A1. As for the polling device, thetransmitting antenna is designed as a rotating spaced loop, and thereceiving antenna as a simple frame. The orientation of transponderantennas arranged on the underbodies of motor vehicles is adjusted tothe orientation of the polling antennas or to the strength distributionof their field such that on the transponder side, the coils wound asflat coils on a rectangular parallelepiped have horizontal or verticalantenna surfaces standing vertically one on top of another.

An antenna system for arrangement in the outer surface of an airplane,especially as a direction-finding antenna, is described in GB A 719526.In a first embodiment, a winding is wound on a rod made of a material ofhigh permeability and the rod is inserted into a slot of the outersurface of the airplane. According to another embodiment, rods made of amaterial of high permeability are inserted in depressions of themetallic surface of the airplane and they face with one end a coil arrayinserted into a window of the metallic surface. Anotherdirection-finding antenna for airplanes, in which a direction-findingantenna consisting of two crossed air core coils is arranged in themetallic surface of an airplane behind a window covered by a dielectricplate, has been known from GB A 2024522. These prior-art arrays fordirection-finding antennas for airplanes require that the metallicsurface of the airplane be interrupted at the site of the antenna. Inaddition, there are restrictions concerning the nature of the materialof the metallic surface, which shall not be magnetic.

Besides applications with transponders located in an extensivelyundisturbed environment, e.g., with transponders carried by persons,transponder arrays on electrically conductive, especially metallicsurfaces with nonuniform orientation of the transponders and objectswith respect to a polling device are of considerable significance,especially in automatization engineering for the identification ofobjects.

SUMMARY AND OBJECTS OF THE INVENTION

The basic object of the present invention is to provide advantageoustransponder arrays with a transponder antenna arranged on anelectrically conductive surface as well as advantageous embodiments oftransponders for this.

A transponder array according to the present invention includes asupport body formed as a flat body with a small height compared withtransverse dimensions of the support body. A coil is wound on thesupport body with a plurality of coil turns. The coil turns cover aportion of a surface of the support body and are wound around thesupport body to form a longitudinal axis of the coil orientedsubstantially in parallel to a plane of the flat body. The coil forms atransponder antenna arranged on an electrically conductive surface withthe antenna coil generating a magnetic field having a principaldirection forming an angle of less than 45° with the conductive surfaceand preferably less than 15 degrees.

The principal direction of the magnetic field (director) of the coils isdetermined in the known manner by the surface normal of the coil surfacein the case of flat coils and by the longitudinal axis of the coil inthe case of elongated coils.

It is seen that good field coupling and consequently a reliable dataexchange are guaranteed with the transponder arrays according to thepresent invention with an extensive freedom in terms of the arrangementand the orientation of the antennas of the polling device. The presentinvention takes advantage of the fact that a polling signal emitted bythe antenna of the polling device has a nearly disappearing magneticfield component in the direction of the surface normal and, comparedwith this, a substantially stronger magnetic field component in parallelto the conductive surface in the vicinity of the electrically conductivesurface, extensively independently from the orientation of thetransmitting antenna of the polling device. The transponder arraysaccording to the present invention utilize this property of the field bytheir orientation with respect to the conductive surface and arrangementon this surface in an especially advantageous manner. In the case of thedivision of the transponder antenna into a plurality of coil sections,e.g., for transmitting and receiving, the orientation applies to allcoil sections.

The various features of novelty which characterize the invention arepointed out with particularity in the claims annexed to and forming apart of this disclosure. For a better understanding of the invention,its operating advantages and specific objects attained by its uses,reference is made to the accompanying drawings and descriptive matter inwhich preferred embodiments of the invention are illustrated.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is view of a transponder arranged on a metallic surface with aircore coil;

FIG. 2 is a view of a transponder array on a support pipe;

FIGS. 3A and 3B are two views of another transponder array;

FIG. 4 is a view of a ferrite antenna arranged on a metallic surface;

FIGS. 5A and 5B are two views of a transponder array with a ferriteantenna;

FIG. 6 is a view of a preferred embodiment of a transponder with asection of a coil;

FIG. 7 is a top view of a transponder according to FIG. 6 with fasteningmeans;

FIG. 8 is a cross-section through the transponder according to FIG. 7.

FIG. 9 is a view of a transponder array at an object; and

FIG. 10 is a sectional view showing the position of a transponder Tfastened to an object O.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to the drawings, FIG. 1 shows an oblique view of an array witha transponder on a metallic and electrically conductive surface M. Inthe example shown, the transponder comprises an antenna A1 designed as aflat air core coil, which is wound, e.g., approximately rectangularly,as well as a transponder electronic unit E, which is electricallyconnected to the antenna via leads Z. The antenna A1 and the electronicunit E are preferably arranged on a common support body T, which isdesigned, e.g., as a flat plastic card, or they are embedded in such asupport. They are mechanically stabilized and protected, and can behandled in a simple manner as a result. The antenna is fastened to themetallic surface M, i.e., by bonding the support body to this surface,in which the surface spanned by the antenna A1 forms an angle w1 ofpreferably 90°0 with the metallic surface M. The angle w1 may also havevalues of <90° to w1>45°, while the function of the array is stillsatisfactory. The principal direction of the magnetic field of the coilextending at right angles to the antenna surface now forms an angle of<45° with the surface M and preferably extends in parallel thereto. Thedistance between the metallic surface M and the section of the air corecoil A1 located closest to the surface is small, preferably <20 mm. Sucha distance may be obtained, e.g., by means of a coating of the metallicsurface, an edge area of the support body T located outside the coilsurface, or the means for fastening the coil or the support body on thesurface, etc. The air core coil of the antenna A1 has, preferably on theside facing the metallic surface, an edge adapted to the course of thissurface, i.e., especially a straight edge section extending in parallelto the surface for a flat metallic surface. The coil A1, the transponderelectronic unit E, and leads Z are physically and electrically spacedfrom the conductive surface M as shown in FIG. 1.

FIG. 2 shows a transponder array with a support body T of the type shownschematically in FIG. 1, in which a transponder is fastened to a flatsurface of a metal pipe R such that a straight edge section of the aircore coil of the antenna A1 extends essentially along the center line ofthe pipe surface at a short distance from same and the surface spannedby the air core coil stands essentially vertically on the pipe surface.

For a metallic construction as in FIG. 2 with an angle formed by twometal surfaces MA and MB, another advantageous transponder array, inwhich two edge sections of the air core coil extend in parallel to thetwo metal surfaces forming the angle and simulate the angle, is shown inFIG. 3A with the direction of view in parallel to the plane of the coiland in FIG. 3B with the direction of view at right angles to the planeof the coil. The surface spanned by the air core coil stands essentiallyvertically on the two metal surfaces MA, MB.

An array according to the present invention for embodying thetransponder antenna as an elongated coil SL, especially as a ferritecoil, i.e., as an elongated coil with a ferrite core FK, is shownschematically in an oblique view in FIG. 4. The ferrite coil A2 isarranged on or at a short distance from the metallic surface M such thatthe longitudinal axis B (director) of the coil extends in parallel tothe metallic surface M. With a still satisfactory function of the array,the longitudinal axis of the coil may also be inclined against themetallic surface and form an acute angle of <45° with same. The ferritecoil is advantageously held by a support body, not shown, which may alsobe the support of the transponder electronic unit.

For a transponder array with a ferrite coil according to FIG. 4, FIG. 5Aschematically shows a side view with the direction of view at rightangles to the coil director B and FIG. 5B shows one with the directionof view in parallel to the coil director B. In the examples shownschematically, the cross section of the coil is approximately round.Analogously to the flat coil design, it is again advantageous in thecase of an elongated coil for the circumferential line of the elongatedcoil to have a section that is parallel to the surface on the side ofthe elongated coil facing the metallic surface.

The exchange of signals between the transponder and a polling devicetakes place via an alternating magnetic field, wherein the antennas A1and A2 are used as the transmitting antenna and the receiving antenna,respectively. The same coil sections, or completely or partiallyseparated coil sections may be used for the case of transmission andreception. Different frequencies are preferably provided fortransmission and reception. The power for the operation of thetransponder may also be transmitted in the known manner via thealternating field emitted by the transmitting antenna PA of the pollingdevice PD.

The relative orientation of the transponder antenna and of the antennaof the polling device requires at least one position with good fieldcoupling. In polling systems with relative movement between the pollingdevice and the transponder array, this is given in conjunction with theorientation according to the present invention of the transponderantennas and with the field effect of the metallic surface for nearlyany relative orientation, so that there is a high degree of freedom fordesigning the systems.

The explanations given for a flat coil and for an elongated coil alsoapply analogously to coils and coil sections of a short overall length.

FIGS. 6 through 9 show a preferred embodiment of a transponder forarrangement on a metallic surface.

The transponder shown schematically in FIG. 6 has a flat support body Kof an essentially rectangular shape with the length l, the width b andthe thickness h. The thickness h of the support body K is advantageouslysubstantially smaller than its length l and width b, i.e. h<<l, b. Acoil array SP with a plurality of coil turns are wound on the supportbody such that the course of the turns is essentially at right angles tothe long sides (l) and the longitudinal axis of the coil (director,principal direction of the magnetic field during current flow throughthe coil array) is essentially parallel to the long sides. Only asection of the coil array is shown. The coil array preferably extendsover the entire length of the support body with the exception of areashaving fastening means. The coil surface has a small overall height dueto the small thickness h of the support body, so that the entire coilsurface can be arranged in the especially effective area close to themetallic surface of an object if the transponder is fastened flat onthis surface. The coil array may comprise a single coil or a pluralityof coil sections, e.g., for different coils or coil combinations intransmission operation and in reception operation. The height h of thesupport body is preferably in the range of 1 to 5 mm, the width b ispreferably in the range of 75 to 80 mm, and the length l is in the rangeof 5-80 mm.

The support body preferably consists of a nonconductive material,especially plastic and/or ferrite. The material of the support body mayalso contain ferromagnetic material, in which case measures of a knownnature are to be taken, if necessary, to suppress eddy currents. Thesupport body is preferably composed of a plurality of layers, whichenclose and surround the transponder electronic assembly unit E (FIGS. 2and 3).

Fastening means are provided at the support body of the transponder forfastening the transponders on an object, e.g., on the surface of ametallic container, as is schematically shown in FIG. 4 or 9. Thesupport body is not covered by the winding of the coil in the area ofthe fastening means. The coil SP and the transponder electric unit E arephysically and electrically spaced from the conductive surface M asshown in FIGS. 7 and 9. The transponder-side fastening means may bedesigned either in a form corresponding to the object-side means orpreferably in an object-independent form. An advantageous example forthe first form of the fastening means are openings in the support bodyK, which are attached and fastened, e.g., riveted to pins or the likealready present on the surface of the object to be equipped with thetransponder. The openings may be prepared already during themanufacturing process of the support body.

Metal spikes suitable for welding are advantageously integrated withinthe support body K, e.g., cast in or inserted later, for theobject-independent form of the fastening means. The metal spikes makepossible a rapid and reliable fastening by welding to the metallicsurface of the object and may also penetrate for this purpose anonmetallic protective coating that may possibly be present on themetallic surface of the object.

The fastening means are preferably arranged on the support body in edgeareas of the support body, e.g., in corners of an essentiallyrectangular support body or in mounting straps joining the coil-carryingmiddle part of the support body.

FIGS. 7, 8 and 9 show as examples two different types of fasteningmeans. Metal spikes D are inserted, e.g., cast in, in an edge area ofthe support body not wound with the coil SP in the left-hand halves ofFIGS. 7 and 9, and the tips of these spikes, which project from thesupport body, are welded to a metallic surface M of an object by, e.g.,stud welding. The design of the fastening means as a mounting strap Lwith an opening P, which is pushed over a pin ST prepared on the object,is shown in the right-hand half of the figure. The transponder is fixedon the object by flattening, bending over, etc. of the pin ST. Atransponder electronic assembly unit embedded in the support body isdesignated by E. The windings of the coil are shown only partially inFIG. 9 for clarity's sake. Contact elements for connecting the coilarray to the electronic assembly unit E are not shown, either.

A plurality of fastening elements on one transponder may be of the sametype or may belong to different types.

The transponder according to the present invention makes it possible todesign mechanically insensitive transponder arrays. Welding to thesupport body via metallic elements and/or the continuation of thesupport body in the form of mounting straps make possible an especiallysimple fastening to the object.

The surface of the transponder, which faces away from the object in themounted state, is preferably designed as a printable surface, e.g., bymeans of an additional layer applied over the windings of the coil,which also acts as a protective layer at the same time. The transpondermay also be inserted into an open or closed housing for fastening and/orfor protection. If the coil is designed as an air core coil, it may beinserted into a support housing having a mounting sleeve.

While specific embodiments of the invention have been shown anddescribed in detail to illustrate the application of the principles ofthe invention, it will be understood that the invention may be embodiedotherwise without departing from such principles.

What is claimed is:
 1. A transponder array comprising: an electricallyconductive surface; a transponder antenna arranged on said electricallyconductive surface with an antenna coil generating a magnetic field, aprincipal direction of said magnetic field forming an angle of less than45° with said conductive surface, said transponder antenna beingelectrically insulated from said electrically conductive surface; atransponder electronic assembly unit electrically connected to saidtransponder antenna to form a circuit electrically insulated from saidelectrically conductive surface, said transponder antenna and saidtransponder electronic assembly are designed to be powered via analternating field emitted by a transmitting antenna of a polling device.2. A transponder array in accordance with claim 1, wherein: saidmagnetic field forms an angle less than 15 degrees with said conductivesurface.
 3. A transponder array in accordance with claim 1, wherein:said coil is a flat air core coil, with a coil surface arranged at rightangles to said conductive surface.
 4. A transponder array in accordancewith claim 3, wherein: said coil has a substantially straight edgesection and said section extends along said conductive surface.
 5. Atransponder array in accordance with claim 1, wherein: said coil isformed from elongated coils and a longitudinal axes of said elongatedcoils are oriented substantially parallel to said conductive surface. 6.A transponder array in accordance with claim 1, wherein: said coilincludes a ferrite core.
 7. A transponder array in accordance with claim1, further comprising: a housing connected to said antenna and formed ofnonconductive material.
 8. A transponder array in accordance with claim1, wherein: said coil includes transmitting and receiving coils.
 9. Atransponder array in accordance with claim 1, further comprising: asupport body formed as a flat body with a small height compared withtransverse dimensions of said flat body, said antenna coil being woundon said support body with a plurality of coil turns, said coil turnscovering a portion of a surface of said support body and being woundaround said support body to form a longitudinal axis of said coiloriented substantially in parallel to a plane of said flat body. 10.Transponder in accordance with claim 9, wherein: said support bodyincludes fastening means on another portion of said surface, saidanother surface being not covered by said antenna coil.
 11. Transponderin accordance with claim 9, wherein: said support body includes a middlepart formed substantially rectangular in transverse dimensions, saidsupport body includes fastening means for fastening said support body toan object surface, said fastening means including mounting strapsextending from said middle part.
 12. Transponder in accordance withclaim 11, wherein: said fastening means includes an opening through saidsupport body.
 13. Transponder in accordance with claim 9, wherein: saidantenna coil includes a plurality of coil sections having asubstantially same orientation.
 14. A transponder array in accordancewith claim 1, further comprising: a support body having a planar shapewith a length, width and height, said height being less than said lengthand width, said antenna coil being wound on said support body with alongitudinal axis of said antenna coil being substantially parallel tosaid planar shape of said support body.
 15. A transponder arraycomprising: an electrically conductive surface; a transponder antennaarranged on said electrically conductive surface with an antenna coilhaving a magnetic field, a principal direction of said magnetic fieldforming an angle of less than 45° with said conductive surface, saidtransponder antenna being physically and electrically spaced from saidelectrically conductive surface; a transponder electronic assembly unitelectrically connected to said transponder antenna to form a circuitelectrically insulated from said electrically conductive surface. 16.The transponder array in accordance with claim 15, further comprising: asupport body mounted on said electrically conductive surface, saidtransponder antenna and said transponder electronic assembly beingmounted on said support body.
 17. The transponder array in accordancewith claim 16, wherein: said transponder electronic assembly is mountedin said support body.
 18. The transponder array in accordance with claim17, wherein: said transponder antenna is wound around said support body;said transponder antenna and said transponder electronic assembly aredesigned to be powered via an alternating field emitted by atransmitting antenna of a polling device.
 19. The transponder array inaccordance with claim 16, wherein: said transponder antenna and saidtransponder electronic assembly are designed to be powered via analternating field emitted by a transmitting antenna of a polling device.